1. Field of the Invention
Pallet trucks with hydraulic lift are used in industry for lifting and transporting loaded pallets and for unloading same at various locations.
2. Description of the Prior Art
The pallet truck includes a hydraulic jack supporting a frame carrying a pair of forwardly extending forks or a platform. Specifically it includes a lift cylinder supporting the frame and the connected forks or platform and a pump cylinder for providing pressurized hydraulic fluid to the lift cylinder. One commercial device which I invented is illustrated and described in the Israel patent application No. 55,148 published in Israel on Feb. 27, 1981. The application is entitled "Dual Rate Jack System for Lift Trucks" and is owned by Korr Metal, Ltd. The pallet truck hydraulic lift described therein employs a hydraulic jack of the type wherein the handle for the pallet truck is pivotally mounted upon the lift cylinder or base and is provided with a connection with the pump cylinder or pump piston so that pivotal movements of the handle actuates the pump cylinder. The forks of the pallet truck at their forward ends have retractable support rollers which are operated by suitable linkage. Upon activation of the lift cylinder raising the frame, the linkage lowers the rollers pivotally with respect to the forks. Such activation lifts the forks into engagement with the under surface of a loaded pallet. Further pumping action of the handle elevates the frame and forks thereby lifting the pallet off of the ground surface for transporting it to another location.
Other pallet truck hydraulic jack assemblies and related prior art lift devices are shown in the following U.S. Pat. Nos.:
2,049,335; 7-28-36, Stephens PA1 2,309,138; 1-26-43, Quayle PA1 2,461,212; 2-8-49, Hanna PA1 3,462,167; 8-19-69, Rateau PA1 2,488,521; 11-22-49, Barrett PA1 2,993,703; 7-25-61, Paradise PA1 3,118,107; 6-8-65, Quale PA1 3,119,627; 1-28-64, Klumb PA1 3,286,985; 11-22-66, Edera PA1 3,567,240; 3-2-71, Brassington PA1 3,608,922; 9-28-71, Best et al PA1 3,701,211; 10-31-72, Best PA1 3,757,523; 9-11-73, Resuggan PA1 3,775,027; 11-27-73, Craft PA1 3,817,546; 6-18-74, Suguira PA1 3,843,147; 10-22-74, Fredricson PA1 3,940,338; 2-24-76, Btyntse, et al.
It is well known that a hydraulic pallet truck for lifting and transporting of pallets and heavy loads has the following basic elements: a hydraulic jack, a frame, steering wheels, and load rollers. The hydraulic jack is comprised of a handle operated pump mounted on a base plate under which is mounted a vertical pivot axle for the articulated steering wheels, and two concentric cylinders with dual diameter and a dual rate lifting piston. Such are described in the aforementioned Israeli patent application.